Aqueous dispersions of epoxy resins have been known for many years. However, the performance of these dispersions as elements of coatings has been viewed as inferior to their solvent borne counterparts. It is known that the surfactants employed to render the epoxy component emulsifiable such as nonylphenol ethoxylates, alkylphenol initiated poly(oxyethylene) ethanols, alkylphenol initiated poly(oxypropylene) poly(oxyethylene) ethanols, and block copolymers containing an internal poly(oxypropylene) block and two external poly(oxyethylene) ethanol blocks readily migrate to surface interfaces where, it is speculated, they deleteriously affect film performance.
Moreover, as aqueous dispersions of epoxy resins have become more widely used in industry, improved handling properties such as storage stability are required. The storage stability of many water borne epoxy dispersions degrades over time due to the presence of amine nitrogen atoms in the surfactant molecules. As the pH of water borne dispersions increases over 9.8, the storage stability can no longer be measured in years, but rather is measured in months.
It would also be desirable to decrease the particle size of the solids, or decrease the amount of surfactant required at a given solids level, or to disperse solids at a given particle size using less surfactant. Often, a larger amount of surfactant needed to decrease the particle size and effectively disperse the solids in water leads to increased pH and reduced storage stability. Decreasing the surfactant level to control the pH causes an increase in particle size.